This invention relates to a process for making a large cell size alkenyl aromatic polymer foam structure with 1,1-difluoroethane. The invention further relates to a foamable gel capable of being expanded to form such a foam structure.
Alkenyl aromatic polymer foam structures have been used extensively commercially in floral and craft applications. The most desirable of such foam structures are typically closed-cell, and further are of relatively large cell size, i.e. 0.3 to 3.0 millimeters.
Due to environmental concerns, it would be desirable to blow large cell size alkenyl aromatic polymer foam structures with a blowing agent having a low ozone depletion potential. One such blowing agent is 1,1-difluoroethane (HFC-152a). HFC-152a is relatively economical, and is readily-available commercially.
In making an alkenyl aromatic polymer foam structure of relatively large cell size, one skilled in the art might select an environmentally-acceptable blowing agent having relatively high solubility in the alkenyl aromatic polymer. High solubility would be sought after because, as a general principle, blowing agents with relatively high solubility in a particular polymer usually produce foam structures with relatively large cell sizes. Blowing agents of relatively low solubility usually produce foam structures having relatively small cell size. Thus, it would not be expected that a blowing agent of relatively low solubility, such as HFC-152a, in an alkenyl aromatic polymer would produce a foam structure of relatively large cell size.
Surprisingly, it has been found that a large cell alkenyl aromatic polymer foam structure can be blown using HFC-152a as a primary blowing agent. Further, the foam structure blown with HFC-152a has high heat distortion temperature properties and low impact strength characteristics.